Ocular torsion may be a useful barometer of exotropia

This prospective study elucidated for the first time the distribution of ocular torsion in intermittent exotropia and found a positive correlation between the amount of ocular torsion and the severity of exotropia.

The authors used digital nonmydriatic fundus photography to analyze the distribution of ocular torsion in 150 patients with intermittent exotropia between 4 and 15 years of age and another 150 age-matched normal controls without strabismus. They analyzed two different angle parameters: the larger disc-foveal angle of the two eyes and the sum of the disc-foveal angles of the two eyes.

Approximately one third of subjects with intermittent exotropia had ocular torsion, although mostly extorsion, in one or both eyes. The average disc-foveal angle was 6.13 ± 4.16 degrees, which was significantly larger than that of the control subjects without strabismus.

Both angle parameters correlated with the amount of exotropia and the degree of stereopsis, although the larger disc-foveal angle showed relatively stronger correlation compared with the sum of the disc-foveal angles.

The authors write that based on these findings, it seems reasonable to presume that intermittent exotropia sometimes may be associated with significant ocular torsion in one or both eyes, especially when binocular fusion is defective. This assumption also is supported by the work of various researchers.

The authors note the relatively strong correlation between the laterality of a more frequently deviating eye and the size of the disc-foveal angle. The side of the more frequently deviating eye could be predicted to some degree by which eye had the larger disc-foveal angle, that is, the larger amount of excyclotorsion. Thus, it seems appropriate to assume that the ocular divergence of the nonpreferred eye may result in excyclotorsion of the eye, whereas fusional vergence may require incyclotorsional movement of that eye.

They also note the relatively strong correlation between stereopsis and ocular torsion. Because stereopsis is a key indicator of the degree of fusional control in patients with intermittent exotropia, it may be said that observing ocular torsion could be a useful supplementary tool in evaluating and monitoring the degree of fusion in patients with intermittent exotropia.